Process for recovering metals and metal compounds from mined ore and other metal-bearing raw source materials

ABSTRACT

A filter cake, including a first metal in an insoluble form and/or filtrate comprising Cr in a soluble form, obtained by a method involving filtering an aqueous slurry of a metal-bearing raw source material comprising the first metal in an insoluble form, soluble and/or insoluble Cr in a Cr bearing material as a second metal, and organic and inorganic compounds, after adjusting the pH of the slurry to an alkaline pH sufficient to convert soluble Cr present to an insoluble form and selectively leaching the Cr by adding a leaching agent in an amount sufficient to convert Cr to a soluble form while the first metal remains in the slurry in an insoluble form.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 12/770,134filed Apr. 29, 2010 which claims the benefit under 35 USC 119(e) ofprovisional application No. 61/174,205 filed Apr. 30, 2009 and No.61/293,419 filed Jan. 8, 2010, all of which are fully incorporatedherein by reference.

BACKGROUND

A. Field

The present invention relates to a method for selectively recovering ametal, groups of metals, and/or metal compound(s) from a metal-bearingraw source material containing chromium (Cr).

B. Related Art

Industrial, mining, and manufacturing processes generate large amountsof metal-bearing raw source material on daily basis. This metal-bearingraw source material includes mining ores, ore concentrates, wasteproducts, residues and byproducts. Metal-bearing raw source materialoften contains valuable nonferrous metals such as chromium (Cr), nickel(Ni), copper (Cu), cobalt (Co), tin (Sn), zinc (Zn), molybdenum (Mo),manganese (Mn), lead (Pb), cadmium (Cd), vanadium (V), as well asprecious and platinum group metals including silver (Ag), gold (Au),palladium (Pd), platinum (Pt), rhodium (Rh), ruthenium (Ru), osmium(Os), and iridium (Ir).

The disposal of metal-bearing raw source material containing thesemetals raises serious environmental and business concerns on a globallevel due to the hazardous nature, potential toxicity, and risk to humanhealth posed by the presence of these metals. The costs associated withthe disposal of hazardous metal-bearing raw source material in theabsence of metal reclamation are enormous. In this regard, recovery ofmetals from metal-bearing raw source material not only would reduce thevolume and cost of disposal, but the recovered metals could be resold orreused to provide substantial economic value. The expenses andenvironmental impact associated with disposing of metal-bearing rawsource material, along with the economic value of the incorporatedmetals, has generated interest in how to treat and recover metals frommetal-bearing raw source material.

Current methods for treating and recovering metals from metal-bearingraw source material, however, are often inefficient and expensive toimplement. It has been particularly challenging to treat and recovermetals from metal-bearing raw source material that contains Cr, as Cr isdifficult to separate from other metals and metal compounds.

For example, vitrification is a proven technique in the disposal andlong-term storage of nuclear waste. However, the presence of Crdramatically increases the bulk of the nuclear waste. In order toeconomize and reduce the quantity of nuclear waste, the Cr content ishydrometallurgically separated and removed, thereby decreasing the totalamount of nuclear waste to be vitrified. See Rapko et al., “SelectiveLeaching of Chromium from Hanford Tank Sludge 241-U-108”, PacificNorthwest National Laboratory, PNNL-14019, article prepared for the U.S.Department of Energy under Contract DE-AC06-76L01830. Rapko et aldisclose that the Cr can be selectively leached from the nuclear wastethrough an oxidative alkaline leaching process. The process, however,utilizes expensive reactants and is not concerned with the recovery oreconomic value of other metals that might be present in the nuclearwaste. The primary objective of Rapko et al. is to effectively reducethe vitrification cost by reducing the quantity of nuclear waste to bevitrified. The removal of the Cr component from the nuclear wastesatisfies this objective by reducing the final quantity of waste thatmust be vitrified, thus lowering the overall cost of processing.

U.S. Pat. No. 5,200,088 describes a process for removing hexavalentchromium (Cr(VI)) from a waste product. This patent suggests that themost hazardous form of chromium is Cr(VI) and that the presence ofCr(VI) in the waste product must be reduced to a few parts per million(ppm) or less before the waste product can be discarded. In accordancewith the process described in this patent, the Cr(VI) in the wasteproduct is converted by treating the waste product with an alkali metaldithionite to reduce the Cr(VI) to trivalent chromium (Cr (III)). Theresult is a soluble material that forms a precipitate at reduced pH. Theprecipitate containing the Cr(III) can then be separated from theremaining waste product. However, the patent does not reveal anyinterest in the recovery or separation of other metals that may bepresent in the Cr-bearing waste.

U.S. Pat. No. 4,162,294 describes a method for recovering Cr and atleast one other metal from a metal-bearing raw source materialcontaining Cr. In particular, the method involves chlorinating a wastesludge containing Cr, aluminum (Al), Cu, Zn, and Ni to oxidize the Crinto a soluble form and to obtain an insoluble component that containsthe Al, Cu, Zn, and Ni; separating the Cr in soluble form from theinsoluble component with a fixed bed anion exchanger; and separating theAl, Cu, Zn, and Ni present in the insoluble component through anelaborate series of liquid-liquid extractions and precipitation steps.

However, ion exchange is relatively costly, slow, and cumbersome to use.In order to be effective, the Cr-bearing material being treated must bepassed through a significant amount of ion-exchange resin, usually inthe form of a filter bed, making it effective, in most cases, fortreating only small volumes of wastewater. Thus, ion exchange would beimpractical as an initial step for separating metals from complexmetal-bearing raw source material. Furthermore, the series ofliquid-liquid extractions and precipitation steps is also inefficient.When the ion exchange step and series of liquid-liquid extractions andprecipitation are used in combination, the method is particularlyinefficient and expensive to execute.

While the above publications focus on the removal of Cr, or the recoveryof Cr and other metals with complicated and expensive processes, none ofthem are seen to disclose a method capable of selectively recovering atleast one metal from a metal-bearing raw source material containing Crin an efficient, relatively low cost manner.

SUMMARY

The present invention is based on the discovery of an efficient andeffective method for selectively recovering at least one metal from ametal-bearing raw source material containing Cr in a soluble orinsoluble form.

In a preferred embodiment of the invention, Ni is also recovered from ametal-bearing raw source material containing Ni and Cr.

More specifically, in accordance with a first aspect of the invention, amethod for selectively recovering a metal from a metal-bearing rawsource material comprises:

-   -   a) mixing with an aqueous medium a metal-bearing raw source        material comprising a first metal in an insoluble form, soluble        and/or insoluble Cr in a Cr bearing material as a second metal,        and organic and inorganic compounds to obtain a slurry        comprising the first metal in an insoluble form, soluble and/or        insoluble Cr in a Cr bearing material and the organic and        inorganic compounds;    -   b) adjusting the pH of the slurry to an alkaline pH sufficient        to convert soluble Cr to an insoluble form;    -   c) optionally adding a first oxidizer to the slurry to        facilitate subsequent oxidation steps;    -   d) selectively leaching the Cr by adding a leaching agent in an        amount sufficient to convert Cr to a soluble form while the        first metal remains in the slurry in an insoluble form;    -   e) filtering the slurry to obtain a filter cake comprising the        first metal in an insoluble form and a filtrate comprising Cr in        a soluble form;    -   f) recovering the filter cake comprising the first metal in an        insoluble form and/or filtrate comprising Cr in a soluble form.

In accordance with another aspect of the invention, the first metal isNi.

According to another aspect of the invention, Ni and Cr are selectivelyrecovered from a metal-bearing raw source material in a processcomprising:

-   -   a) mixing with an aqueous medium a metal-bearing raw source        material comprising Ni compound(s) in an insoluble form as a        first metal, insoluble Cr compound(s) as a second metal, and        organic and inorganic compounds to obtain a slurry comprising Ni        in an insoluble form, insoluble Cr, and the organic and        inorganic compounds;    -   b) adjusting the pH of the slurry to facilitate subsequent        oxidation steps;    -   c) optionally adding a first oxidizer to the slurry to oxidize        the organic and inorganic compounds,    -   d) adding a second oxidizer to the slurry in an amount        sufficient to oxidize the Cr into a soluble form while the Ni        remains in the slurry in an insoluble form;    -   e) filtering the slurry to obtain a filter cake comprising Ni in        an insoluble form and a filtrate comprising Cr in a soluble        form;    -   f) recovering the filter cake comprising Ni in an insoluble        form; and    -   g) optionally recovering the filtrate comprising Cr in a soluble        form.

In accordance with another aspect of the invention, Ni and Cr arerecovered from Ni and Cr bearing materials by a method comprising:

-   -   a) mixing with an aqueous medium a metal-bearing raw source        material comprising Ni compound(s) in insoluble form, insoluble        Cr compound(s) and organic and inorganic compounds to obtain a        slurry comprising the first metal in an insoluble form,        insoluble Cr, and the organic and inorganic compounds;    -   b) adding a hydroxide to the slurry to raise the pH of the        slurry to 12.0-12.5 and in an amount sufficient to form chromium        hydroxide (Cr(OH)₃), chromium oxide (Cr₂O₃), or mixtures        thereof;    -   c) adding a first oxidizer comprising calcium hypochlorite to        the slurry in an amount sufficient to oxidize said organic and        inorganic compounds;    -   d) adding a second oxidizer comprising MnO₄ ⁻ to the slurry in        an amount sufficient to react with the Cr(OH)₃, Cr₂O₃, or        mixtures thereof as follows:

2Cr(OH)₃+4MnO₄ ⁻=2CrO₄ ⁻²+MnO₂+3O₂ or  (1)

2Cr₂O₃+4MnO₄ ⁻=4CrO₄ ⁻²+8MnO₂+3O₂,  (2)

wherein CrO₄ ⁻² is soluble and remains in the slurry to provide achromate solution and MnO₂ is an oxide precipitate;

-   -   e) filtering the slurry to obtain a filter cake comprising Ni in        an insoluble form and filtrate comprising chromate;    -   f) recovering the filter cake comprising Ni;    -   g) treating the filtrate comprising Cr(VI) with acid in an        amount sufficient to obtain an acidic solution comprising        Cr(VI);    -   h) adding sodium metabisulfite to the acidic solution in an        amount sufficient so that the Cr(VI) reacts with the sodium        metabisulfite to obtain a reaction as follows:

2CrO₄ ⁻²+2Na₂S₂O₅=2Cr⁺³+4NaSO₄+O₂  (3)

-   -   i) adjusting pH of the acidic solution with a hydroxide in an        amount sufficient to obtain a reaction as follows:

Cr⁺³+3NaOH=Cr(OH)₃+3Na⁺  (4)

wherein Cr(OH)₃ is a Cr hydroxide precipitate;

-   -   j) filtering the solution comprising Cr(OH)₃ to obtain a Cr(OH)₃        filter cake; and    -   k) recovering the Cr filter cake.

Additional details and variations of the described processes embodyingthe invention will be described in the detailed description below.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a flowchart exemplifying a method for recovering Ni and Crfrom a Ni/Cr raw material in accordance with the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The phrase “selectively leach” as used herein means to wash, extract, orperform a chemical reaction to separate a soluble element or compoundfrom an insoluble material.

The phrase “insoluble form” means an element in free form or compoundincapable of or that resists dissolving in a particular solvent.

A “metal-bearing raw source material” is any material that contains ametal. This includes waste, residue, ore, ore concentrate, byproduct,processed, and/or unprocessed material.

The phrase “plating sludge” is a hydroxide sludge, which has been formedduring the treatment of waste liquor, metal plating, or other metalfinishing processes and waste waters which may or may not be dehydrated.

A “Ni/Cr raw material” is a material that contains Ni and Cr and/or Niand Cr compounds and potentially other metals of value.

The phrase “predetermined criteria” means a previously determinedstandard that a metal-bearing raw source material must meet regarding aspecific economic and elemental threshold, before being processed inaccordance with the present invention.

The present invention relates to a method for selectively recovering ametal from a metal-bearing raw source material. The method involvesmixing in an aqueous medium a metal-bearing raw source materialcontaining (i) a first metal in an insoluble form, (ii) insoluble and/orsoluble Cr in a Cr bearing material as a second metal, and (iii) organicand inorganic compounds to obtain a slurry. The slurry contains thefirst metal in an insoluble form to be recovered, the Cr bearingmaterial, and the organic and inorganic compounds.

The first metal remains insoluble throughout the method. The first metalis preferably in an insoluble form that is incapable of or resistsdissolving so that less than 1.0% of the first metal is in a solubleform at any given time during the method.

The pH of the slurry is then adjusted to facilitate the efficientoxidation of Cr in subsequent steps. The pH is preferably adjusted to analkaline state, and more preferably to a pH of 12.0 to 12.5 to convertsoluble Cr to insoluble Cr.

A first oxidizer is optionally added to the slurry to oxidize extraneousorganic and inorganic compounds present in the slurry. The Cr in aninitially insoluble form can then be selectively leached from insolublecomponents that may be present in the slurry by adding a leaching agentin an amount sufficient to obtain Cr in a soluble form. While the Crwill be converted to a soluble form, the first metal remains in theslurry in an insoluble form. The slurry may then be filtered to obtain afilter cake containing the first metal in an insoluble form and afiltrate containing Cr in a soluble form.

The filter cake containing the first metal in an insoluble form and/orfiltrate comprising Cr in a soluble form may then be recovered.

The filter cake optionally contains additional metals (i.e., a thirdmetal) that were present in the raw material and recovered along withthe first metal. The other base, precious, and platinum group metalsthat may be recovered include but are not limited to Ni, Cu, Co, Sn, Zn,Mo, Mn, Pb, Cd, V, Ag, Au, Pd, Pt, Rh, Ru, Os, and Ir

In a preferred embodiment of this invention, the first metal is Ni.

FIG. 1 depicts in a flowchart a preferred method for recovering Ni andCr from a Ni/Cr raw material. The selected Ni/Cr raw material (110) maybe any material that contains Ni and Cr, such as metal bearing ores andconcentrates, metal plating and finishing sludges, industrial material,processed material, and/or unprocessed material.

Prior to processing, selection of the Ni/Cr raw material is determinedby testing (100) to determine whether the Ni bearing groups satisfypredetermined criteria. For example, the Ni/Cr raw material is tested todetermine whether a sufficient amount of metals are present in the Ni/Crraw material. The Ni/Cr raw material preferably contains 5% by weight Niand 5% by weight Cr, and more preferably 10-20% by weight of Ni and10-15% by weight of Cr. The Ni/Cr raw material also can be tested todetermine whether any deleterious constituents (e.g., Hg) are present.It is important to note that as economic conditions vary, improvedconditions (i.e., metal price increases, processing chemicals costdecreases, etc.) may permit wider ranges of Ni/Cr content to beeconomically processed by this invention. All economic conditions aswell as metals content (primary and secondary) must be considered on anindividual basis when determining the viability of acceptance of the rawfeedstock materials.

Ni/Cr raw material that satisfies the predetermined acceptance criteriais then approved for processing (200). Any material that does not meetthe predetermined acceptance criteria based on metal content and otherconstituent content and/or economic considerations maybe designated asnonconforming material (210). For example, when the Ni/Cr raw materialcontains mineral or metal constituents which exhibit deleteriouscharacteristics that prevent the material from being safely oreffectively processed, the material may be rejected as non-conformingmaterial or it could be used as an ingredient in a formulation withother conforming materials (220).

According to one aspect of the process, the nonconforming Ni/Cr rawmaterial is formulated and combined with other conforming Ni/Cr rawmaterial that has been found to satisfy the predetermined acceptancecriteria (300).

In yet another aspect of the process, Ni/Cr raw material identified asnon-conforming material may be combined as an ingredient with otherNi/Cr raw materials to provide a batch-formulation of material that doessatisfy the predetermined process criteria. For example, a first lot ofNi/Cr raw material identified as “non-conforming” material whenprocessed by itself and unacceptable to be processed individually, maybe formulated with another raw material to provide a batch of Ni/Cr rawmaterial that does satisfy the predetermined criteria.

A slurry is then formed by adding to an aqueous medium the Ni/Cr rawmaterial batch or the formulated Ni/Cr material batch. In oneembodiment, the aqueous medium is tap water. In another embodiment, theaqueous solution is any recycled water (940) or water recycled from aprevious cycle using the described method (950 or 955). The Ni/Cr rawmaterial present in the slurry at this stage will be in an amount of1-10% by weight, and more preferably 2-5% by weight of the slurry.

The slurry is adjusted to an alkaline pH (e.g., a pH of 12) by theaddition of a compound that accepts protons, for example caustic soda(50% NaOH) (400). Cr is present in the alkaline slurry in both theCr(III) and Cr(VI) oxidation states. In its Cr(III) oxidation state, Cris in the form of a Cr precipitate such as chromium hydroxide (Cr(OH)₃)or chromium oxide (Cr₂O₃). In its Cr(VI) oxidation state, Cr is in analkaline soluble-form, such as chromate (i.e., a salt containing theanion Chromic Acid (H₂CrO₄ or CrO₄ ²⁻). The Ni is present in the slurryin an insoluble form.

In order to separate the Ni in insoluble form from a Cr precipitate, thealkaline slurry is treated with an oxidizer. The oxidizer is preferablya permanganate (MnO₄ ⁻) compound, such as, for example, potassium orsodium permanganate. The MnO₄ ⁻ is preferably added in excess. Thesolution preferably has an Oxidation Reduction Potential (ORP) of +300to +400, which is preferably maintained for 1-3 hours and morepreferably for 2 hours so that a sufficient amount of MnO₄ ⁻ can reactwith Cr in an insoluble form. The oxidizer converts Cr(III) to its moresoluble form of Cr(VI) to form a chromate or dichromate solution. Thereaction is exemplified as follows:

for Cr(OH)₃:

2Cr(OH)₃+4MnO₄ ⁻=2CrO₄ ²⁺+4MnO₂+3O₂  (1)

for Cr₂O₃:

2Cr₂O₃+8MnO₄ ⁻=4CrO₄ ²⁺+8MnO₂+3O₂.  (2)

The chrome (Cr(VI)) compounds formed (e.g., CrO₄ ⁻²/Cr₂O₇ ⁻²) aresoluble, whereas the MnO₂ compounds are insoluble. By converting theCr(III) in the slurry to a more soluble form of Cr (i.e., Cr(VI)), theCr can be selectively leached from the slurry.

For example, a first and second oxidizer can be added sequentially tothe slurry. Oxidizers capable of converting Cr(III) to Cr(VI), arerelatively expensive. To lower the process cost, a less expensiveoxidizer may be first added to the alkaline slurry (i.e., a firstoxidizer). The first oxidizer is added in an amount sufficient to reactwith extraneous organic and inorganic compounds (e.g., compounds notcontaining Cr) present in the slurry. An “amount sufficient’ ispreferably an amount wherein the first oxidizer is added in excess asindicated by a potassium iodide or starch test paper providing a colorchange when excess oxidizer is present. The first oxidizer is preferablya hypochlorite, such as calcium hypochlorite, ferrate, or ozone.

Once any extraneous organic and inorganic compounds have reacted withthe first oxidizer, a more costly oxidizer capable of converting Cr(III)to Cr(VI) (i.e., the second oxidizer) can be added. In other words, thefirst oxidizer may be regarded as a “sacrificial” oxidizer that reactswith the extraneous organic and inorganic compounds. This allows for agreater amount of the more costly second oxidizer to react with the Crof the Cr bearing material present in the slurry. By doing so, smalleramounts of the more costly second oxidizer will be required during theprocess, reducing the process cost. The second oxidizer is preferablyadded in excess to provide an ORP as discussed above. For example,approximately two pounds of MnO₄ ⁻ can be added for each pound of thefirst oxidizer that was added to the alkaline slurry (500).

Once the reaction is complete, the slurry can then be filtered (600) toobtain a filter cake containing Ni and insoluble oxides such as MnO₂(610). The Cr remains in a Cr(VI) solution (700) and can be optionallyrecovered as discussed below. Filtering methods and devices known tothose skilled in the art can be used for this filtration step.

The filter cake containing Ni is optionally batched with other filtercakes (620) previously obtained in accordance with the method discussedabove. The filter cake may then be further concentrated (630) bydehydration using methods and devices known to those skilled in the art.

The filter cake may also contain additional metals that were present inthe raw material and that may be recovered along with the Ni. The otherbase, precious, and platinum group metals in the filter cake include butare not limited to Ni, Cu, Co, Sn, Zn, Mo, Mn, Pb, Cd, V, Ag, Au, Pd,Pt, Rh, Ru, Os, and Ir (i.e., third metals).

The Ni concentrate and other metals obtained from the process areoptionally further separated by adding the Ni concentrate and othermetals to a smelter. Smelting is a form of extractive metallurgy; itsmain use is to produce a metal from an ore. Smelting uses heat and achemical reducing agent to change the oxidation state of the metal ore.

The resulting Cr(VI) solution (700) is preferably processed in one oftwo ways. In one embodiment, the Cr(VI) solution is processed (710, 720)into a chromium hydroxide filter cake (1000). In another embodiment, theCr(VI) solution is processed (750, 760, 780) to obtain a concentratedCr(VI) solution or crystalline Cr(VI) powder (2000).

When processed into a filter cake (1000), the Cr(VI) solution is reducedfrom Cr⁺⁶ to Cr⁺³ to form Cr hydroxide (710) by adjusting the pH of theCr(VI) solution to an acidic pH (e.g., 1.0 to 2.0) with an acid, such assulfuric acid (H₂SO₄) or nitric acid (HNO₃) (710) and then adding areducing agent such as sodium metabisulfite (Na₂S₂O₅) to the solution.The resulting solution is maintained with stirring for preferably 30minutes to 2 hours, and more preferably 1 hour to assure that asufficient amount of reducing agent reacts with the Cr. The reaction isexemplified as follows:

2CrO₄ ⁻²+2Na₂S₂O₅=2Cr⁺³+4NaSO₄+O₂.  (3)

Following the Cr reduction, the pH of the solution is raised to form analkaline solution (e.g., having a pH of 9.0). The solution is preferablyraised by adding a compound that accepts protons, for example causticsoda (50% NaOH) (710). The reaction is exemplified as follows:

Cr⁺³+3NaOH=Cr(OH)₃+3Na⁺.  (4)

A Cr hydroxide precipitate is formed (710) and is preferably recoveredin the form of a filter cake. In a preferred embodiment, the solution Crprecipitate is recovered with a filter press (720) to produce a chromiumhydroxide filter cake (1000). Filtering methods known to those skilledin the art can be used for this filtration step.

The chromium hydroxide filter cake (1000) may contain elevatedconcentrations of sulfate resulting from the production of NaSO₄ duringthe previous chrome reduction reaction. Water soluble NaSO₄ is retainedin the interstitial waters of the filter cake. A low sulfate chromiumhydroxide product is more commercially desirable, therefore the chromiumhydroxide filter cake (1000) containing elevated concentrations ofsulfate can be optionally further processed by re-slurrying (1010) thechromium hydroxide filter cake (1000) with a solids solution (e.g. 10%solid solution) to leach out the sulfate, and recovering a secondchromium hydroxide filter cake with a filter press (1020). Water solublesulfate compounds and other water soluble compounds are contained in thefiltrate and removed from the filter cake.

An alternate sulfate reduction method involves “washing” (1040) theinitial filter cake, while still contained in the filter press, bypassing a sufficient volume of fresh water through the press to reducethe sulfate content to a desirable level. This alternate washingprocedure is preferably used when lesser amounts of sulfate need to beremoved.

These optional slurrying and filtration steps produce a chromiumhydroxide filter cake (1030) with a higher purity.

The resulting filtrate may then be further treated (800) and recycled(950) as the aqueous solution in the slurrying step (400).

As noted above, the Cr(VI) solution may be processed into a concentratedCr(VI) solution or powder (2000). The Cr(VI) solution may beconcentrated by ion exchange (750) and/or concentrated by evaporation(780). In this aspect of the invention, the Cr(VI) solution is eitherdirectly (740) subjected to an evaporation/crystallization process (780)from the selective leaching process (700) or alternatively, passed fromthe selective leaching procedure (700) through an ion exchange column(750) to selectively remove the Cr. The Cr(VI) is loaded onto column bypassing the Cr(VI) solution over the column. The aqueous fractionexiting the column is substantially free of Cr and can be re-used (955).

When the Cr(VI) has been loaded onto the column (750), the ion exchangeresin may be regenerated by eluting the resin with a hydroxide solution,such as a 5% NaOH solution (760). The eluted Cr(VI) solution is thenpreferably further concentrated. In one aspect of the invention, theeluted Cr(VI) solution is concentrated 5-10 fold (760).

The eluted Cr(VI) solution may then be evaporated (780) with the use ofa heating source such as waste heat exchange (770) or a heater (775) toobtain a concentrated Cr(VI) solution or crystalline Cr(VI) powder(2000). Evaporating and drying methods and devices known to thoseskilled in the art can be used for this evaporation step.

In yet another embodiment, the present invention relates to acomposition produced by the above-identified method, wherein saidcomposition preferably comprises Ni or Cr.

The foregoing description of the invention has been presented describingcertain operable and preferred aspects. It is not intended that theinvention should be so limited since variations and modificationsthereof will be obvious to those skilled in the art, all of which arewithin the spirit and scope of the invention.

1. A filter cake produced by a method for selectively recovering a metalfrom a metal-bearing raw source material, the method comprising: a)mixing with an aqueous medium a metal-bearing raw source materialcomprising a first metal in an insoluble form, soluble and/or insolubleCr in a Cr bearing material as a second metal, and organic and inorganiccompounds to obtain a slurry comprising the first metal in an insolubleform, soluble and/or insoluble Cr in a Cr bearing material and theorganic and inorganic compounds; b) adjusting the pH of the slurry to analkaline pH sufficient to convert soluble Cr present to an insolubleform; c) optionally adding a first oxidizer to the slurry to facilitatesubsequent oxidation steps; d) selectively leaching the Cr by adding aleaching agent in an amount sufficient to convert Cr to a soluble formwhile the first metal remains in the slurry in an insoluble form; e)filtering the slurry to obtain a filter cake comprising the first metalin an insoluble form and a filtrate comprising Cr in a soluble form; f)recovering the filter cake comprising the first metal in an insolubleform and/or filtrate comprising Cr in a soluble form; and comprisingsaid first metal.
 2. A filtrate produced by the method for selectivelyrecovering a metal from a metal-bearing raw source material, the methodcomprising: a) mixing with an aqueous medium a metal-bearing raw sourcematerial comprising a first metal in an insoluble form, soluble and/orinsoluble Cr in a Cr bearing material as a second metal, and organic andinorganic compounds to obtain a slurry comprising the first metal in aninsoluble form, soluble and/or insoluble Cr in a Cr bearing material andthe organic and inorganic compounds; b) adjusting the pH of the slurryto an alkaline pH sufficient to convert soluble Cr present to aninsoluble form; c) optionally adding a first oxidizer to the slurry tofacilitate subsequent oxidation steps; d) selectively leaching the Cr byadding a leaching agent in an amount sufficient to convert Cr to asoluble form while the first metal remains in the slurry in an insolubleform; e) filtering the slurry to obtain a filter cake comprising thefirst metal in an insoluble form and a filtrate comprising Cr in asoluble form; f) recovering the filter cake comprising the first metalin an insoluble form and/or filtrate comprising Cr in a soluble form;and comprising Cr in a soluble form.
 3. The method for selectivelyrecovering nickel (Ni) and chromium (Cr) from a metal-bearing raw sourcematerial, comprising: a) mixing with an aqueous medium a metal-bearingraw source material comprising Ni compound(s) in an insoluble form as afirst metal, insoluble and/or soluble Cr compound(s) as a second metal,and organic and inorganic compounds to obtain a slurry comprising Ni inan insoluble form, insoluble and/or soluble Cr, and the organic andinorganic compounds; b) adjusting the pH of the slurry to facilitatesubsequent oxidation steps; c) adding a first oxidizer to the slurry tooxidize the organic and inorganic compounds, d) adding MnO₄ ⁻ to theslurry in an amount sufficient to oxidize the Cr into a soluble formwhile the Ni remains in the slurry in an insoluble form; e) filteringthe slurry to obtain a filter cake comprising Ni in an insoluble formand a filtrate comprising Cr in a soluble form; f) recovering the filtercake comprising Ni in an insoluble form; g) optionally recovering thefiltrate comprising Cr in a soluble form; wherein step g) furthercomprises: (I) treating the filtrate comprising Cr in a soluble formwith an acid to obtain an acidic solution; (II) adding a reducing agentto the acidic solution while mixing to reduce the Cr in a soluble formto an insoluble form; (III) adjusting the pH of the acidic solution to abasic solution to form a solution comprising Cr hydroxide precipitate(Cr(OH)₃); and (IV) filtering the solution comprising Cr(OH)₃precipitate to obtain a filter cake comprising Cr(OH)₃ and a basicsolution.
 4. The method according to claim 3, further comprising (V)reslurrying the Cr(OH)₃ filter cake to wash out sulfates and other watersoluble compounds, and (VI) filtering the slurry comprising washedCr(OH)₃ filter cake to obtain a second Cr(OH)₃ filter cake.
 5. Themethod according to claim 3, further comprising adding a sufficientamount of reducing agent to step (II) to obtain a reaction as follows:2CrO₄ ⁻²+2Na₂S₂O₅=2Cr⁺³+4NaSO₄+O₂.  (3)
 6. The method according to claim5, wherein a sufficient amount of base is added to obtain a reaction asfollows:Cr⁺³+3NaOH=Cr(OH)₃+3Na⁺  (4) wherein Cr(OH)₃ is a precipitate.
 7. Themethod for selectively recovering nickel (Ni) and chromium (Cr) from ametal-bearing raw source material, comprising: a) mixing with an aqueousmedium a metal-bearing raw source material comprising Ni compound(s) inan insoluble form as a first metal, insoluble and/or soluble Crcompound(s) as a second metal, and organic and inorganic compounds toobtain a slurry comprising Ni in an insoluble form, insoluble and/orsoluble Cr, and the organic and inorganic compounds; b) adjusting the pHof the slurry to facilitate subsequent oxidation steps; c) adding afirst oxidizer to the slurry to oxidize the organic and inorganiccompounds, d) adding MnO₄ ⁻ to the slurry in an amount sufficient tooxidize the Cr into a soluble form while the Ni remains in the slurry inan insoluble form; e) filtering the slurry to obtain a filter cakecomprising Ni in an insoluble form and a filtrate comprising Cr in asoluble form; f) recovering the filter cake comprising Ni in aninsoluble form; g) optionally recovering the filtrate comprising Cr in asoluble form; wherein step g) further comprises: passing the filtratecomprising Cr in a soluble form over an ion exchange column, wherein theion exchange column binds Cr and provides a cleaned aqueous fraction,eluting the ion exchange column with a buffer to obtain a fractioncomprising Cr in a soluble form, and optionally concentrating thefraction comprising Cr in a soluble form.
 8. A Cr(VI) product producedby the method according to claim
 7. 9. A filter cake produced by theprocess according to claim 6, wherein the filter cake comprises Cr(OH)₃.10. A method for selectively recovering nickel (Ni) and chromium (Cr)from a metal-bearing raw source material, comprising: a) mixing with anaqueous medium a metal-bearing raw source material comprising Nicompound(s) in insoluble form, insoluble and/or soluble Cr compound(s)and organic and inorganic compounds to obtain a slurry comprising thefirst metal in an insoluble form, insoluble Cr, and the organic andinorganic compounds; b) adding a hydroxide to the slurry to raise the pHof the slurry to 12.0-12.5 and in an amount sufficient to form chromiumhydroxide (Cr(OH)₃), chromium oxide (Cr₂O₃), or mixtures thereof; c)adding a first oxidizer comprising calcium hypochlorite to the slurry inan amount sufficient to oxidize said organic and inorganic compounds; d)adding a second oxidizer comprising MnO₄ ⁻ to the slurry in an amountsufficient to react with the Cr(OH)₃, Cr₂O₃, or mixtures thereof asfollows:2Cr(OH)₃+4MnO₄ ⁻=2CrO₄ ⁻²+MnO₂+3O₂ or  (1)2Cr₂O₃+4MnO₄ ⁻=4CrO₄ ⁻²+8MnO₂+3O₂,  (2) wherein CrO₄ ⁻² is soluble andremains in the slurry to provide a chromate solution and MnO₂ is anoxide precipitate; e) filtering the slurry to obtain a filter cakecomprising Ni in an insoluble form and filtrate comprising chromate; f)recovering the filter cake comprising Ni; g) treating the filtratecomprising Cr(VI) with acid in an amount sufficient to obtain an acidicsolution comprising Cr(VI); h) adding sodium metabisulfite to the acidicsolution in an amount sufficient so that the Cr(VI) reacts with thesodium metabisulfite to obtain a reaction as follows:2CrO₄ ⁻²+2Na₂S₂O₅=2Cr⁺³+4NaSO₄+O₂  (3) i) adjusting pH of the acidicsolution with a hydroxide in an amount sufficient to obtain a reactionas follows:Cr⁺³+3NaOH=Cr(OH)₃+3Na⁺  (4) wherein Cr(OH)₃ is a Cr hydroxideprecipitate; j) filtering the solution comprising Cr(OH)₃ to obtain aCr(OH)₃ filter cake; and k) recovering the Cr filter cake.
 11. A filtercake obtained by the process according to claim 10, wherein the filtercake comprises Ni.
 12. A filter cake obtained by the process accordingto claim 10, wherein the filter cake comprises Cr(OH)₃.
 13. A method forselectively recovering nickel (Ni) and chromium (Cr) from ametal-bearing raw source material, comprising: a) mixing with an aqueousmedium a metal-bearing raw source material comprising Ni in insolubleform, soluble and/or insoluble Cr in a Cr bearing material and organicand inorganic compounds to obtain a slurry comprising the first metal inan insoluble form, soluble and/or insoluble Cr, and the organic andinorganic compounds; b) adding a hydroxide to the slurry to raise the pHof the slurry to 12.0-12.5 and in an amount sufficient to form chromiumhydroxide (Cr(OH)₃) chromium oxide (Cr₂O₃), or mixtures thereof; c)adding a first oxidizer comprising calcium hypochlorite to the slurry inan amount sufficient to oxidize said organic and inorganic compounds; d)adding a second oxidizer comprising MnO₄ ⁻ to the slurry in an amountsufficient to react with the Cr(OH)₃, Cr₂O₃, or mixtures thereof asfollows:2Cr(OH)₃+4MnO₄ ⁻=2CrO₄ ⁻²+MnO₂+3O₂ or  (1)2Cr₂O₃+4MnO₄ ⁻=4CrO₄ ⁻²+8MnO₂+3O₂,  (2) wherein CrO₄ ⁻² is soluble andremains in the slurry to provide a Cr(VI) solution and MnO₂ is an oxideprecipitate; e) filtering the slurry to obtain a filter cake comprisingNi in an insoluble form and a filtrate comprising Cr(VI); f) recoveringthe filter cake comprising Ni in an insoluble form; g) passing thefiltrate comprising Cr(VI) over an ion exchange column, wherein the ionexchange column binds Cr(VI) and provides a cleaned aqueous fraction; h)eluting the ion exchange column with a buffer to obtain a concentratedCr(VI) fraction having Cr in an amount 5-10 fold more than present inthe filtered Cr(VI) solution; and i) recovering a concentrated Cr(VI)fraction.
 14. A filter cake obtained by the process according to claim13, wherein the filter cake comprises Ni.
 15. A Cr(VI) fraction producedby the process according to claim 13, wherein the filter cake comprisesCr.